Ionization measurement instrument



June 12, 1962 R. FUTTERKNECHT IONIZATION MEASUREMENT INSTRUMENT Filed Feb. 16, 1960 INVHV TOR. RUDOLF F UTT ERKN ECH T ATTORNEYS.

n at United States Patent IONIZATION MEASUREMENT INSTRUMENT Rudolf Futterknecht, Stuttgart-Wangen, Germany, as-

signor, by mesne assignments, to Nassau Distributing Company, Inc., New York, N.Y.

Filed Feb. 16, 1960, Ser. No. 9,109 Claims priority, application Germany Feb. 20, 1959 13 Claims. (Cl. 250-83.3)

The present invention relates to an ionization measurement instrument which consists essentially of an ionization chamber filled with an ionizable gas and of a preferably coaxial high-vacuum chamber. The latter contains an electron gun from which an electron beam, which is conducted between electrically charged deflection plates or electrodes emerges against afluorescent screen serving as indicating surface.

Measuring instruments of this type are in principle no longer new. However, for the production of the electrons and the voltages necessary for their acceleration, there are required special voltage sources which are generally located outside the measuring instrument and which are used up relatively rapidly.

In contradistinction to these known ionization measurement instruments, it is a principal object of the invention to provide an ionization measuring instrument in which an electron-beam indicator is produced by an electron gun including a solid containing tritium in bound form as a source of electrons.

This solid containing tritium in bound form is located within a metallic chamber or housing which forms the electron gun and which has an electron emitting opening. The chamber is of such shape that the electrons emerge, focused by the static charges produced by the electrons emerging from the tritium, in the form of a sharply defined beam and are conducted between pairs of deflection plates or electrodes.

In accordance with the invention, the solid containing the bound tritium preferably has the shape of a shallow dish which emits electrons toward both sides. The concave surface of the dish is directed toward the outlet opening of the electron gun. The dish in conjunction with the electrically charged wall of the electron gun housing exerts a focusing action on the emerging electron beam.

As the solid containing tritium in bound form, there can be used a metal which absorbs or adsorbs tritium and which is preferably very thin, for instance a few microns in thickness. This thin metal dish can be mechanically stabilized by a suitable plastic which presents only slight resistance to the emergence of the electrons coming from the bound tritium and which does not produce any substantial slowing-down of the electrons.

The flat layer serving as electron source containing tritium in bound form can also be made of an organic plastic in the molecules of which-at least in part-at least one H-atom is replaced by tritium.

The invention will be better understood from the following description read in conjunction with the single FIGURE of the drawing in which there is shown, more or less schematically, in longitudinal section, one embodiment of an ionization measuring instrument in accordance with the invention.

The measuring instrument consists of a tubular housing having two coaxial cylindrical chambers 1 and 2 separated from each other by a glass wall 3 which serves as an electrically insulating partition. The lower cham- 3,038,995 Patented June 12, 1962 Ice stance which can be excited to photoemission by electrons and which may be metallized in order to lead away disturbing charges. Within the vacuum chamber 2, there is contained the upward tapering metallic housing of the electron gun 4. This housing is supported by an intermediate wall- 14 provided with suitable openings 20. Within the housing of the electron gun 4, there is arranged the dished tritiumcontaining emission electrode 6 which is connected conductively via its lateral support 12 with the metallic inner wall of the vacuum chamber 2. The sidewalls of the chambers 1 and 2 are provided with a conductive metal coating or consist of metal. Support 12 passes through a hole 21 in the wall of gun housing 4.

Within the ionization chamber 1, there is contained the central electrode 11 serving as cathode which is sealed into the partition 3 and which can be temporarily conductively connected with the electron gun 4 by means of an intense externally generated energy field in order that the electrode may be charged to the voltage level of the gun. This temporary connection is indicated schematically by dotted line C.

Between the conductive inner wall of the vacuum chamber 2, and the metallic housing of the electron gun 4, there is located a leak resistor 15 by which, independently of the duration of the emission of tritium electrons, a given voltage difference is maintained between the electron emission electrode 6 (anode) and the inner wall of the vacuum chamber 2 on the one hand and the wall of the electron gun 4 on the other hand.

The dished emission electrode 6 (anode) within the electron gun 4 can consist of a thin metal of the order of magnitude of a few microns. The metal contains tritium in absorbed or adsorbed form, there being preferably used a metal which does not give the tritium off again in gas form upon merely moderate heating. For the stabilizing and stifiening of the thin metal dish 6, suitable plastic coatings can be used which present the least possible resistance to the electrons which emerge at both sides of the dish.

In accordance with the invention, the electron-emitting dished emission electrode 6 can also consist of a suitable organic plastic in the molecules of which-or at least in a part of its moleculesat least one hydrogen (H) atom is in each case replaced by a tritium atom. These plastics which in themselves are non-conductive can be made conductive in known manner by means of a conductive varnish, graphiting, or the like.

Above the mouth or aperture 5 of the electron gun 4, there are located two deflecting plates or electrodes 7 and 8, the left plate 7 being conductively connected with the inner wall of the vacuum chamber 2, by wire 7', while the right plate 8 is conductively connected by the wire 9 with the central electrode 11 in the ionization chamber 1.

The sharply focused electron beam emerging from the upward directed aperture 5 of the electron gun 4 for the focusing of which beam additional apertured diaphragms 22, 23 may be provided within the housing of the electron gun 4, moves in the vacuum chamber 2 between the two dotted lines -17 and 18 which indicate its limit positions.

in order to efiect a measurement, a conductive connection C of very short duration is produced between the housing of the electron gun 4 and the central electrode 11 of the ionization chamber 1 and thus of the deflecting plate 8 connected to electrode 11. This may be done by briefly placing a generator of an intense magnetic, electric or electromagnetic field close to the thin walled housing which will be substantially transparent to this field to generate a flow of free electrons in path P. Thereafter, the instrument is placed in the path of ionizing rays or particles whose intensity is to be measured.

As a result the electron beam is deflected in its outermost left-hand position 17 and thereupon, with decreasing negative charge of the ionization chamber central electrode 11, with respect to the positively charged wall of the ionization chamber 1, gradually travels toward the right. The voltage drop of the central electrode 11 of the ionization chamber 1 within a given period of time serves as measure of the intensity of the ionizing rays and particles entering the ionization chamber. The deflection of the beam visible on screen 13 serves as an indication of ionization of the gas in chamber 1 during the measurement period.

The use of bound tritium as source of electrons for an ionization measuring instrument is of essential importance since the electrons emerging from the tritium only possess such energy that they do not emerge downward out of the electron gun to avoid causing ionization within the ionization chamber. In addition to this, the user of this ionization measuring instrument in accordance with the invention is not subject to radiation injury in view of the low energy of the particles liberated upon the decomposition of tritium (electrons and helium).

It has been previously proposed to use natural or synthetic radioactive substances as electron sources in electron-ray tubes and furthermore to use the static charges produced by the electrons for focusing the electron beam.

The proposals as to the use of radioactive substances were made prior to the recognition of the danger of radioactive radiations such as obtained from atomic bomb tests. On the other hand, heretofore no one has proposed the idea of using gaseous tritium as source of electrons in an ionization measuring instrument. Tritium was not considered as a possible source of electrons because it does not have a solid form suitable for the production of a source of electrons, and also because the energy of the electrons emitted by tritium is so slight that it is completely slowed down, even by very thin layers of matter.

The previously proposed instruments which use natural radioactive substances or strontium 90 as radiation sources cannot be used in accordance with modern scientific knowledge as pocket instruments due to the required radiation protection walls which are of very great weight, in addition to the fact that in the case of the destruction of an instrument containing such a radioactive substance, the danger of contamination with radioactive substances is above the maximum permissible limit.

What I claim is:

1. An ionization measuring instrument, comprising a casing having a gas filled ionization chamber and a vacuum chamber separated by a dividing wall, deflection electrodes for an electron beam disposed in said vacuum chamber, an electron gun in said vacuum chamber, a source of a beam of electrons in the form of a solid substance containing tritium located within the electron gun, a central electrode in the ionization chamber conductively connected with one of said deflection electrodes to charge said central electrode, said gun being temporarily conductively connectable by external means with said central electrode for making a measurement of ionization of the gas in said ionization chamber.

2. An ionization measuring instrument according to claim 1, wherein the tritium containing solid has the form of a shallow dish which emits electrons at both of its sides, said dish having a concave surface directed toward an outlet opening of said electron gun, said concave surface exerting a focusing action on said electron beam in cooperation with walls of said gun while in a charged condition.

3. An ionization measuring instrument according to claim 1, wherein said solid substance is a thin metal only a few microns in thickness.

4. An ionization measuring instrument according to claim 2, wherein said dish is a metal body having a thickness of only a few microns.

5. An ionization measuring instrument according to claim 4, wherein said dish is stifiened by a plastic material which presents only slight resistance to the passage of electrons from the bound tritium to avoid slowing down substantially the electrons emitted by the tritium.

6. An ionization measuring instrument according to claim 1, wherein the tritium containing solid is an organic plastic having molecules in which at least one hydrogen atom is replaced by a tritium atom.

7. An ionization measuring instrument according to claim 2, wherein said dish is a plastic shell rendered electrically conductive by a conductive coating, said plastic having molecules in each of which at least one hydrogen atom is replaced by a tritium atom.

8. An ionization measuring instrument according to claim 1, there being a leak resistor connected between said electron gun and said source of electrons.

9. An ionization measuring instrument according to claim 2, wherein said electron gun has an electrically conductive housing, there being a leak resistor connected between said housing and said dish.

10. An ionization measuring instrument according to claim 1, wherein said vacuum chamber and said ionization chamber have metallized walls connected by electrically conductive means to said dish.

11. An ionization measuring instrument according to claim 1, wherein said electron gun has an electrically conductive housing, the temporary conductive connection between said central electrode and said housing being producible by said external means to charge said central electrode negatively to a certain voltage level while said one deflection electrode is simultaneously charged to the same voltage level for deflecting said electron beam.

12. An ionization chamber according to claim 10, wherein another deflection electrode for the electron beam is connected electrically with the metallized wall of said vacuum chamber.

13. An ionization chamber according to claim 1, where in said electron gun is provided with intermediate apertured walls for concentrating said beam of electrons therein.

No references cited. 

